1. Field of the Invention
The present invention relates to a technique of optical alignment and more particularly a technique for aligning a polymer film, a method for aligning a liquid crystal with a controllable pretilt angle by using the polymer aligned-film and a liquid crystal display(LCD) employing the above techniques.
2. Related Art
A flat panel display is an important device in a television having a small size and a large scale screen and a portable terminal. Specially, an LCD is widely used as information display device in view of low addressing voltage, high contrast ratio, cheap cost, high reliability to the solar light and good interface to an integrated circuit.
So as to manufacture the LCD having an uniform brightness and high contrast ratio, the liquid crystal inserted between a pair of substrates in the LCD should be arranged in one direction. Generally, alignment films are formed on the opposite surfaces of a upper substrate and a lower substrate, thereby aligning the liquid crystal in one direction.
A general method for aligning the liquid crystal molecules is a surface treatment, specifically rubbing. A polyimide resin is coated on a surface of the substrate and then rubbed with a fabric, thereby forming a straight groove. The liquid crystal is aligned along the groove.
However, since rubbing is performed after forming the polyimide on the glass substrate having a color filter or a thin film transistor(TFT) array, the color filter or the TFT array beneath the substrate can be subjected to mechanical or electrical damage. Accordingly, reproduction of the process is not good. Also, the LCD manufactured by the rubbing method has a narrow viewing angle. In order to solve the narrow viewing angle, there is a technique for forming multi-domain. The process for forming the multi-domain using the rubbing method is complicated.
In the LCD, by using the rubbing method, it is not easy to control a pretilt angle of the liquid crystal which is an important factor for the response time and the contrast ratio of the LCD. Therefore, recently, a method for adjusting the pretilt angle, without rubbing, has been actively studied.